you need to check the ampdraw on your brushless system, its usually in the packaging somewhere, but at a guess i'd say 4.5t novak was pretty high.
then lipo wise you take the capacity in mAh/1000 * C rating to get the ampage
ie 4200mAh with a 40C rating would give you (4200/1000)*40=168amps
not easy to find a lipo with these big numbers in a stick pack style but there are some on evilbay from HK, i just ordered one branded as a 'silverback'